A document published by the Internal Revenue Service (IRS) that provides information on income tax rules for individuals who have retired from federal service. Retirement benefits for federal employees are paid by either the Civil Service Retirement System (CSRS) or the Federal Employee Retirement System (FERS). IRS Publication 721 covers survivor benefits, thrift savings plans, rollovers, federal estate taxes and the Simplified Method for calculating annuity benefits.

Part of the benefits paid out is tax free, because they are contributions made by the employee, while the rest of the benefits are considered taxable. The tax-free part is a fixed number; the taxable part is the difference between the full amount and that which is not taxed.